Aluminum Phosphate Ceramics for Waste Storage

ABSTRACT

The present disclosure describes solid waste forms and methods of processing waste. In one particular implementation, the invention provides a method of processing waste that may be particularly suitable for processing hazardous waste. In this method, a waste component is combined with an aluminum oxide and an acidic phosphate component in a slurry. A molar ratio of aluminum to phosphorus in the slurry is greater than one. Water in the slurry may be evaporated while mixing the slurry at a temperature of about  140 - 200 ° C. The mixed slurry may be allowed to cure into a solid waste form. This solid waste form includes an anhydrous aluminum phosphate with at least a residual portion of the waste component bound therein.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Nos.60/537,207 (entitled “Aluminum Phosphate Ceramics For Hazardous WasteStorage” and filed 18 Jan. 2004); 60/499,453 (entitled “AluminumPhosphate Ceramics For Hazardous Waste Storage” and filed 2 Sep. 2003);and 60/450,563 (entitled “Phosphate-Bonded Ceramic StabilizationChemistry Applied To High Level Radioactive Wastes” and filed 26 Feb.2003). The entirety of each of these applications is incorporated hereinby reference, as is the entirety of concurrently filed U.S. applicationSer. No. ______, which names D. Maloney and A. Wagh as inventors, isentitled “Method of Waste Stabilization with Dewatered Chemically BondedPhosphate Ceramics,” and is identified by Attorney Docket No. CH2M.38.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

The United States Government has rights in this invention pursuant toContract No. W-31-109-ENG-38 between the U.S. Department of Energy andthe University of Chicago, representing Argonne National Laboratory, andCRADA No. 0200201 between Argonne National Laboratory and CH2M HILL,Inc.

TECHNICAL FIELD

The present invention generally relates to methods and apparatus forprocessing waste and to solid waste forms. Aspects of the invention haveparticular utility in connection with processing radioactive waste andother hazardous waste streams for long-term storage and/or disposal.

BACKGROUND

A number of solutions have been proposed for long-term storage anddisposal of various waste streams. The options for disposing of aparticular type of waste will depend in part on the nature of the waste.Safely and cost-effectively disposing of hazardous wastes, for example,presents a difficult challenge. Such hazardous waste streams may includeone, two, or more of aqueous liquids, heterogeneous debris, inorganicsludges, heavy metals, organic liquids, contaminated soils, andradioactive byproducts of nuclear power generation or weaponsmanufacture. (As used herein, the term “hazardous waste” may includenuclear materials that may not be classified as “hazardous waste” underpertinent state, federal, or local laws or regulations.) High-levelradioactive waste also presents significant processing difficulties.

One of the approaches proposed for long-term stabilization and storageof hazardous wastes, particularly radioactive wastes, is vitrification.Unfortunately, vitrification requires very high temperature processing.For example, U.S. Pat. No. 6,258,994 suggests vitrification of waste,including radioactive waste, at about 1,050-1,250° C. and states thatconventional vitrification processes take place at, e.g., 1,4000° C.Heating the waste to such high temperatures is quite costly. Manyhazardous waste streams include hazardous materials that volatilize at“light-off” temperatures well below 1,000° C. Some hazardous componentsof radioactive waste streams, for example, have light-off temperaturesas low as 200° C., with mercury chloride volatilizing at about 200-225°C. As a consequence, vitrifying a waste including mercury chloride orother low light-off temperature materials generates a secondaryhazardous waste stream requiring further processing.

Others have proposed immobilizing or stabilizing hazardous wastes inceramics that can be formed at lower temperatures. InternationalPublication No. WO 92/15536 (the entirety of which is incorporatedherein by reference), for example, suggests immobilizing hazardous wastein hydrated cement. A variety of chemically bonded phosphate ceramic(CBPC) products have been used to stabilize hazardous waste. Forexample, U.S. Pat. Nos. 5,645,518 and 5,846,894 and U.S. PatentApplication Publication 2003/0092554 (the entirety of each of which isincorporated herein by reference) suggest various CBPC compositionsuseful for low-temperature waste processing. Conventional CBPCssuggested for waste processing are typically hydrous ceramics such asmagnesium potassium phosphate hexahydrate (MgKPO₄.6H₂O) or newberryite(MgHPO₄.3H₂ 0).

Hydrated cements and CBPCs have proven to be quite useful in handling avariety of waste streams. Unfortunately, conventional cements and CBPCshave proven somewhat problematic for stabilizing radioactive wastes,particularly high-activity radioactive wastes. Radioactive wastestypically radiate γ rays and α, β, and n particles, which can decomposethe bound water in hydrous cements and CBPCs in a process referred to asradiolysis to generate hydrogen gas. This hydrogen gas pressurizesstorage containers or other waste forms, which can cause the containersor waste forms to fracture and admit intrusion of moisture from air,groundwater, or other elements. Under some circumstances, water canreflect nuclear radiation, increasing the chance that highly activeradioactive wastes could “go critical” if the waste loading is not keptartificially low.

The significant volume and weight of the final waste form are alsoshortcomings of waste storage employing CBPCs and hydrated cementcompositions. If the waste stream is dry or is a liquid waste withrelatively low water content, additional water must be added to form theceramic matrix. This increases both the volume and the weight of thefinal waste form. Even for liquid waste streams with ample water, thewater chemically bound in the system can add significantly to the totalweight; water comprises over 40% of the molecular weight of magnesiumpotassium phosphate hexahydrate, for example. The additional weight andvolume can increase the already significant costs of storing anddisposing of radioactive wastes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of aspects of a waste processingapparatus in accordance with one embodiment of the invention.

FIG. 2 is a schematic illustration of an acidic phosphate productionsystem in accordance with another embodiment of the invention.

FIG. 3 is a schematic illustration of a solid waste form in accordancewith a further embodiment of the invention.

DETAILED DESCRIPTION A. Overview

Various embodiments of the present invention provide solid waste formsand methods for processing waste. The following text discusses aspectsof the invention in connection with FIGS. 1-3 to provide a thoroughunderstanding of particular embodiments. A person skilled in the artwill understand, however, that the invention may have additionalembodiments, or that the invention may be practiced without several ofthe details of the embodiments shown in FIGS. 1-3.

One embodiment of the invention provides a method of processing wastethat includes combining a waste component with an aluminum oxide and anacidic phosphate component in a slurry that comprises water. The wastecomponent may comprise hazardous waste and a molar ratio of aluminum tophosphorous in the slurry may be greater than one. Water in the slurrymay be evaporated while mixing the slurry at a functional temperature ofabout 140-200° C. The mixing may be terminated and the mixed slurry maybe allowed to cure into a solid waste form comprising an anhydrousaluminum phosphate with a residual portion of the waste component boundtherein.

A method of producing a stable waste form in an alternative embodimentincludes reacting an aluminum oxide with an acidic phosphate componentin a first slurry. The first slurry is at least partially dried at afirst temperature to form a phosphate precursor. The phosphate precursorand the waste are mixed in a second slurry at a second temperature ofabout 106-175° C. while allowing water in the second slurry toevaporate. After at least a majority of the water in the second slurryis evaporated, the mixed second slurry may be allowed to cure into asolid waste form. The solid waste form includes a remaining portion ofthe aluminum oxide distributed in a matrix comprising an anhydrousaluminum phosphate and at least a portion of the waste.

Another embodiment of the invention provides a method of producing astable, low-volume waste form from a radioactive material. In accordancewith this embodiment, the radioactive material is mixed with an aluminumoxide and an acid phosphate to form a slurry. A molar ratio of aluminumto phosphorous in the slurry is between about 2 and about 5 and thealuminum oxide may comprise hydrous alumina, anhydrous alumina, oraluminum hydroxide. The slurry may be heated to a first temperature thatis no greater than about 200° C., but is at least as great as adissolution temperature of the aluminum oxide with the acidic phosphate.While mixing the slurry, water is evaporated from the slurry at a secondtemperature of about 140-175° C. until a substantial majority of thewater is evaporated. After the water evaporation, the resultantevaporated product may be allowed to cure as a solid waste formcomprising aluminum oxide particles and at least a portion of theradioactive waste in a matrix comprising substantially anhydrousaluminum phosphate.

A solid waste form in accordance with still another embodiment includesa matrix comprising a substantially anhydrous aluminum phosphate and aphosphate of a heavy metal. Radioactive material and aluminum oxideparticles are distributed in the matrix.

For ease of understanding, the following discussion is subdivided intothree areas of emphasis. The first section discusses waste processingapparatus in accordance with selected embodiments of the invention. Thesecond section outlines methods in accordance with other aspects of theinvention. The third section outlines aspects of solid waste forms inaccordance with further embodiments of the invention.

B. Waste Processing Apparatus

Select embodiments of the invention provide waste processing systemssuitable for use with a variety of waste streams. FIG. 1 schematicallyillustrates a waste processing system 10 in accordance with oneparticular embodiment of the invention. The waste processing system 10includes a waste processing vessel 20 having walls 22 defining a vesselinterior 24. The vessel 20 can be open, as shown, or closeable. In oneembodiment, the waste processing vessel 20 is a conventional storagetank of the type currently used to hold some liquid wastes, e.g., liquidradioactive wastes. Depending on the nature of the waste beingprocessed, it may be advantageous to effectively enclose the wasteprocessing vessel 20 within a “glove box” 12 or similar enclosure tolimit the spread of radioactive material or other hazardous componentsof the waste.

An acidic phosphate may be delivered to the vessel interior 24 from aphosphate supply 40 via a phosphate delivery line 42. An aluminum oxidemay be delivered to the vessel interior 24 from an aluminum oxide supply46 via an aluminum oxide delivery line 48. Waste from a waste supply 50may be delivered via a waste delivery line 52 to the vessel interior 24.In select embodiments, the waste processing system 10 includes a CBPCprecursor supply 90, e.g., a source of magnesium oxide (MgO). A CBPCline 92 may deliver the precursor to the vessel interior 24. If needed,water from a water supply 56 may be delivered to the vessel interior 24via a water delivery line 58.

A mixing system 30 may be used to mix the materials added to the vesselinterior 24. The mixing system 30 of FIG. 1 includes a motor 32, whichmay be positioned outside the glove box 12 to limit contamination,coupled to a mixer 35 via a releasable coupling 34. The mixer 35 in FIG.1 is schematically illustrated as a series of laterally-extending bladesor paddles, but this is solely for purposes of illustration and anysuitable shape may be used. The coupling 34 may be adapted toselectively engage the shaft of the mixer 35 for rotation by the motor32, yet allow the mixer 35 to be readily decoupled from the motor 32.For example, the coupler 34 may provide a spline connection between themixer 35 and the motor 32, allowing the mixer 35 to be selectivelycoupled or decoupled from the motor 32 by axial movement. In otherembodiments, the mixing system 30 shown in FIG. 1 may be replaced by anyof a variety of systems that will effectively mix the materials added tothe vessel interior 24.

The waste processing system 10 may also include a thermal control 60operatively coupled to the glove box 12 and/or the waste processingvessel 20 to control the temperature of the material in the vesselinterior 24. The thermal control 60 may, for example, comprise a fluidjacket for circulating heated or cooled fluid around the vessel 20.Alternatively, the thermal control 60 may comprise a microwave source ora series of infrared heating panels adapted to direct radiation ontoand/or into the vessel 20. In other embodiments, no thermal control 60is used. This may be useful if the reaction in the vessel issufficiently exothermic to heat the contents to the desired temperature.

As explained in more detail below, water may be driven off of thecontents of the vessel interior 24 during processing. If the nature ofthe waste in the waste supply 50 so dictates, the water vapor and anyother gas in the glove box 12 may be delivered to a scrubber 64 via agas line 66. After scrubbing in the scrubber 64 to remove any hazardousvolatile material, the gas may be vented to the atmosphere via a ventline 68.

In some embodiments of the invention detailed below, the processed wasteis allowed to cure in the vessel 20. In other embodiments, it may beadvantageous to remove the mixed components from the vessel 20 beforethey cure, e.g., in a continuous process instead of a batch process. Insuch an embodiment, the contents of the vessel 20 may be delivered to astorage vessel 70 via an outlet 72.

A controller 80 may be used to control aspects of the waste processingsystem 10. The controller 80 may be operatively coupled to one or moreof the mixing system 30, the thermal control 60, the phosphate supply 40or delivery line 42, the aluminum oxide supply 46 or delivery line 48,the waste supply 50 or delivery line 52, the CBPC precursor supply 90 orthe CBPC line 92, and the water supply 56 or delivery line 58. In oneembodiment, the controller 80 comprises at least one computer having aprogrammable processor programmed to control operation of thesecomponents to process the waste in the waste supply 50.

The aluminum oxide and the aluminum oxide supply 46 may comprise any ofa variety of aluminum oxides. Suitable aluminum oxides include, but arenot limited to, anhydrous aluminum oxides (e.g., corrundum, which isAl₂O₃), hydrous aluminum oxides (e.g., gibbsite (Al₂O₃.3H₂O) or böhmite(Al₂O₃.H₂O)), and aluminum hydroxide (Al(OH)₃). The aluminum oxides maybe used in relatively pure form or as components of suitable minerals,e.g., bauxite or kaolin. It has been discovered that aluminosilicatesare insufficiently reactive with acidic phosphates, even concentratedphosphoric acid, at the relevant temperatures to form an aluminumphosphate ceramic in accordance with embodiments of the invention. Thepresence of aluminosilicates in the final waste form is not likely tohave any adverse consequence. When determining the amount of aluminumoxide to be added from the aluminum oxide supply 46, though, only thequantity of the non-alumina silicate aluminum oxides in the aluminumoxide supply 46 should be considered.

The phosphate supply 40 may include any acidic phosphate that is adaptedto react with the aluminum oxide in the aluminum oxide supply 46 toproduce a solid waste form in accordance with aspects of the inventiondiscussed below. If so desired, the acidic phosphate may also have asuitable reaction rate with the CBPC precursor in the CBPC precursorsupply 90. Examples of suitable acidic phosphates include, but are notlimited to, H₃PO₄ (phosphoric acid) and phosphate salts such asphosphate salts of monovalent metals (e.g., K, Na, Li, or Rb). Theformation of such salts and their utilization in various CBPCs arediscussed in U.S. Pat. Nos. 5,830,815 and 6,153,809, the entirety ofeach of which is incorporated herein by reference.

Phosphoric acid can be difficult to handle safely, particularly if theprocessing of the waste is to be conducted in a glove box 12 orsimilarly restrictive enclosure. Phosphates of monovalent metals may becrystalline in form, which can enhance the ease of handling. In anotherembodiment, however, the acidic phosphate in the phosphate supply 40includes, and may consist essentially of, an aluminum hydrophosphate,e.g., AlH₃(PO₄)₂.H₂O, AlH₃(PO₄)₂.3H₂O, and, optionally, additionalaluminum oxide.

The waste in the waste supply 50 can be any of a variety of potentiallyproblematic waste streams, e.g., waste streams (whether specific ormixed) that include one or more of hazardous wastes, industrial wastesother than hazardous wastes, and chemicals other than hazardous wastesthat may have a meaningful environmental impact (e.g., excess nitratesor many organic chemicals). Aspects of the invention have particularutility in connection with processing hazardous wastes. As used herein,the term “hazardous waste” or “hazardous wastes” includes material thatmay or may not be defined as such under applicable laws and regulations,e.g., FERC or CERCLA. Hence, the term “hazardous wastes” is intended toinclude, but is not limited to, high-level radioactive wastes,trans-uranic (TRU) wastes, low-level radioactive wastes, fissionproducts, nuclear materials (e.g., uranium, plutonium, and any otherweapons grade or highly dangerous radioactive or pyrophoric metals),nuclear process byproducts, heavy metals, pyrophoric metals that are notnuclear materials, and toxic organic materials (e.g., PCBs or somepesticides). Unless the context indicates otherwise, the term “hazardouswaste” as used herein is intended to cover both relatively specificwaste streams, e.g., many high-level radioactive wastes, and mixed wastestreams that may include materials not otherwise considered hazardous,e.g., contaminated soils. It is also anticipated that embodiments of theinvention may be used to process hazardous wastes that are solidhazardous wastes, semi-solid hazardous wastes (e.g., sludges), or liquidhazardous wastes, which may include water, acids, oils, or organicsolvents, for example. In one particular example, the hazardous wastecomprises nuclear materials that are solids/powders contaminated withhalogenated salts.

As noted above, the acidic phosphate in the phosphate supply 40 mayinclude an aluminum hydrophosphate. FIG. 2 schematically illustrates aphosphate production system 100 in accordance with an embodiment of theinvention that may be useful for producing aluminum hydrophosphatecompositions. This phosphate production system 100 includes a phosphateproduction vessel 110 having a vessel interior 112. The phosphateproduction vessel 110 may be substantially open, allowing gases (e.g.,water vapor) to exit the vessel 110; in the illustrated embodiment, thevessel 110 is substantially enclosed. A mixer 120 may be positioned atany suitable location within the vessel interior 112 to mix thereactants added to the vessel 110. An acidic phosphate may be deliveredto the vessel 110 from a phosphate supply 130 via a delivery line 132.Aluminum oxide from an aluminum oxide supply 136 may be delivered to thevessel interior 112 via a delivery line 138. If it is necessary to addwater to the contents of the phosphate production vessel 110, it may bedelivered from a water supply 154 via a delivery line 156.

As explained below, it can be advantageous to produce aluminumhydrophosphate in the phosphate production system 100 at a temperatureof 100° C. or less. A thermal control 150 may be operably coupled to thephosphate production vessel 110 to assist in appropriately controllingthe temperature of the reactants in the vessel interior 112. Thisthermal control 150 may be adapted to heat and/or cool the contents ofthe vessel 110. If the phosphate production vessel 110 is sealed, asshown, the pressure in the vessel interior 112 may be monitored and/orcontrolled by a pressure controller 140. Water vapor and any other gaseswithin the vessel interior 112 may be vented, e.g., to atmosphere, via avent line 142. The vent line 142 may include a selectively controllablevent valve 144. The vent valve 144 can be operated directly by thepressure controller 140 or, if so desired, by a more direct link to thecontroller 160. The controller 160 in this embodiment may be similar tothe controller 80 described above.

If aluminum hydrophosphate is produced in the phosphate productionsystem 100 on a batch basis, the phosphate production vessel 110 can beemptied at the end of the batch cycle, e.g., by opening the vessel.Either to ease this removal or for continuous systems, the resultantaluminum hydrophosphate composition may exit the vessel interior 112 viaan outlet line 172. An outlet valve 174 may be included to selectivelyopen or close the outlet line 172. In the illustrated embodiment, theproduct exiting the outlet line 172 is delivered to storage 170. Inother embodiments, the outlet line 172 may instead feed the aluminumhydrophosphate composition directly into the waste processing system 10of FIG. 1. For example, the outlet line 172 of the phosphate productionsystem 100 may function as the acidic phosphate delivery line 42 in thewaste processing system 10.

Suitable aluminum oxides for the aluminum oxide supply 136 include thoselisted above as suitable for the aluminum oxide supply 46 of the wasteprocessing system 10 (FIG. 1). Similarly, suitable acidic phosphates inthe phosphate supply 130 may be substantially the same as thosediscussed above in connection with the phosphate supply 40 of the wasteprocessing system 10 (FIG. 1). In one advantageous embodiment, theacidic phosphate in the phosphate supply 130 comprises phosphoric acid.Phosphoric acid typically is not sold in pure form, but is insteadtypically diluted with water, e.g., an aqueous solution comprising nomore than about 85 weight percent phosphoric acid. In embodimentsemploying phosphate salts, it may be advantageous to add water from thewater supply 154 to the charge of materials in the vessel interior 112.

As explained in more detail below, the aluminum hydrophosphatecompositions produced in the phosphate production system 100 may provideall of the necessary quantities of acidic phosphate and aluminum oxidefor processing waste in the-waste processing system 10 (FIG. 1). In suchan embodiment, the phosphate supply 40 and aluminum oxide supply 46 inthe waste processing system 10 may be combined into a single supply, thecontents of which may be manufactured in the phosphate production system100 of FIG. 2.

C. Methods of Processing Waste

Other embodiments of the invention provide methods of processing wastes,e.g., hazardous wastes. In the following discussion of such methods,reference is made to the waste processing system 10 shown in FIG. 1 andthe phosphate production system 100 shown in FIG. 2. It should beunderstood that this is solely for purposes of illustration and that thefollowing methods are not limited to use of the particular structures orsystems shown in the drawings or discussed above.

In accordance with one embodiment of the invention, acidic phosphatefrom the phosphate supply 40, aluminum oxide from the aluminum oxidesupply 46, waste from the waste supply 50, and, optionally, water fromthe water supply 56 may be added to the waste processing vessel 20 ofFIG. 1. These materials may be mixed with the mixing system 30 to form aslurry, e.g., an aqueous slurry.

The relative proportions of the acidic phosphate, aluminum oxide, andwaste added to the waste processing vessel 20 will depend, at least inpart, on the nature of the materials themselves. For example, one mayadd more of a liquid waste having a high water content than may beappropriate if the waste were a dry waste or had a lower water content.Alternatively, a waste containing aluminum oxide may require lessadditive oxide. It is anticipated that waste loading (i.e., theproportion of waste in the final solid waste form) as high as about 85weight percent (dry weight basis) may work for many types of waste. Forwastes that are likely to leach hazardous materials (e.g., heavymetals), lower waste loadings may be more appropriate. For example, itis anticipated that some heavy metal-bearing waste streams may compriseas much as 70 weight percent of the final solid waste form.

In some embodiments, aluminum and phosphorus may be present in theslurry in any ratio, e.g., one or less than one. It has been foundadvantageous for many applications, though, to have a molar ratio ofaluminum to phosphorus in the slurry greater than one. As explainedbelow, select embodiments employing such ratios can yield solid wasteforms having aluminum oxide particles distributed in an anhydrousaluminum phosphate, which may improve the mechanical properties of thesolid waste form. If the Al:P ratio is too high, though, this can undulydecrease the waste loading capacity of the resultant solid waste form.Hence, Al:P molar ratios of greater than one but no greater than fiveare deemed particularly useful. In select embodiments, the Al:P ratio isat least about two, e.g., about 2-5, with a range of about 2-3 expectedto yield suitable results without unduly increasing the weight of thesolid waste form. As noted above, aluminosilicates are insufficientlyreactive with acidic phosphates to form anhydrous aluminum phosphate inaccordance with embodiments of the invention. Hence, in embodiments ofthe invention that include aluminosilicates in the slurry (whether fromthe aluminum oxide supply 46 or from another source), the Al:P ratio maybe greater than 5, yet have an available Al:P ratio, which excludesaluminosilicates, of no greater than about 5.

As noted above, embodiments of the invention provide solid waste formscomprising anhydrous aluminum phosphates. Even if relatively littlewater is present in the components added to the waste processing vessel20, water may be created or liberated during the reaction between theacidic phosphate and the aluminum oxide. For example, if the aluminumoxide is a hydrous aluminum oxide, e.g., gibbsite, the water bound inthe aluminum oxide may be released. Even if the aluminum oxide in thealuminum oxide supply 46 is anhydrous (e.g., corundum), water may begenerated by the reaction with the acidic phosphate component. Forexample, alumina may react with phosphoric acid generally in accordancewith the following formula:

Al₂O₃+2H₃PO₄→2AlPO₄+3H₂O

Embodiments of the invention producing anhydrous aluminum phosphatematrix may drive this water byproduct from the waste processing vessel20. In the particular waste processing system 10 shown in FIG. 1, thiswater vapor may be vented from a glove box 12 via gas line 66.

The temperature of the reactants in the waste processing vessel 20 maybe controlled with the thermal control 60 to drive off the excess waterin a measured fashion and to control the nature of the resultantreaction product. If one were to mix this slurry at about roomtemperature, as is conventional for most CBPC waste storage systemsknown in the art, the reaction of the aluminum oxide and the acidicphosphate would yield an aluminum hydrophosphate, e.g., AlH₃(PO₄)₂·H₂Oand AlH₃(PO₄)₂·3H₂O. bound in the hydrophosphate can be broken down byradiolysis, generating hydrogen gas. To avoid generating hydrogen in thefinal waste form, the aluminum oxide and aluminum phosphate are allowedto react at an elevated temperature of at least about 100° C. As notedabove, some components of hazardous waste streams, e.g., HgCl, begin tovolatilize at about 200° C. To limit such volatilization, someembodiments of the invention react the aluminum oxide and the acidicphosphate at a temperature of about 100-200° C.

It is believed that having at least some water present in the systemwill propagate the reaction between the aluminum oxide and the acidicphosphate. Particularly for waste streams having relatively low watercontent, temperatures that are too high may drive off all of the waterbefore the aluminum oxide and acidic phosphate have an adequateopportunity to react to form a strong matrix. Accordingly, in someembodiments of the invention, the temperature of the reactants is nogreater than about 175° C., e.g., no greater than about 160° C. In oneadvantageous embodiment, the temperature is between about 100° C. andabout 150° C.

The temperature at which the solubility of the aluminum oxide inphosphoric acid (which may be used as the acidic phosphate) reaches amaximum may depend on the nature of the aluminum oxide. For example,corrundum reaches a maximum solubility in phosphoric acid at about 106°C. Böhmite reaches maximum solubility around 126° C., aluminum hydroxidereaches maximum solubility at about 133° C., and gibbsite reachesmaximum solubility at about 170° C. Hence, in some embodiments of theinvention—especially those that employ phosphoric acid as the acidicphosphate—the temperature of the reactants is at least as great as adissolution temperature of the aluminum oxide, which may be defined as atemperature at which the aluminum oxide reaches or nearly reaches itsmaximum solubility. For example, if the aluminum oxide comprisescorrundum, the temperature of the slurry in the waste processing vessel20 may be about 106-200° C. Temperatures of about 130-200° C., anddesirably about 140-200° C., e.g., about 140-160° C., should be suitablefor many aluminum oxides. In select embodiments, the process takes placeat about 145-155° C.

Some hazardous wastes include heavy metals, e.g., lead, cesium, ortechnetium, that are soluble in water. Most of these heavy metals willreact with an acidic phosphate to form a metal phosphate that issubstantially insoluble in water. This can substantially reduce thelikelihood that heavy metals in the waste being processed will leach outof the resultant solid waste form. If the heavy metal content of thewaste being processed is sufficiently high, it is believed advantageousto allow the acidic phosphate in the slurry to react with the heavymetals to form insoluble phosphates at a lower temperature in an aqueousslurry, which promotes the reaction by maintaining the metals insolution. Thereafter, the temperature may be elevated to promote theformation of the anhydrous aluminum phosphate and driving off the waterin the slurry.

In one exemplary embodiment for processing a waste including a heavymetal component, the slurry may be mixed at a temperature less than 100°C., e.g., between room temperature and 100° C., for at least about tenminutes before the slurry is heated to a temperature above 100° C. asdescribed above. It is anticipated that a time of about 10-15 minuteswill suffice for many waste streams. If so desired, the components maybe mixed in the slurry at about room temperature and the thermal control60 may be used to ramp up the temperature gradually to allow 10-15minutes, for example, below 100° C.

The particular waste treatment system 10 shown in FIG. 1 includes a CBPCprecursor supply 90 adapted to deliver a CBPC precursor to the interior24 of the vessel 20 via CBPC line 92. In some embodiments that areparticular useful for use with some highly acidic wastes, the CBPCprecursor comprises a metal oxide that is capable of reacting with anacidic phosphate to form a CBPC, but may also be adapted to react withother acid components in the waste. In one particular implementation,the CBPC precursor comprises MgO, which is adapted to react with acidicphosphates, as explained above, but is also adapted to react withnitrates (NO₃ ⁻) to form Mg(NO₃)₂, which is less soluble than water inmany other nitrates. The formation of Mg(NO₃)₂ can be promoted by addingthe CBPC precursor to the waste in the vessel interior 24 before addingaluminum oxide or the acidic phosphate to the vessel 20. To promote thisreaction, the mixer 30 may be used to mix the slurry for a period oftime, e.g., 10-15 minutes, to allow the MgO or other CBPC precursor toreact with the nitrates in the waste.

The addition of a CBPC precursor from the CBPC precursor supply 90 canbe advantageous for some highly alkaline wastes, as well. For example,some radioactive waste strings include high levels of nitrates (e.g.,from the use of nitric acid to process spent fuel) and sodium (e.g., theaddition of NaOH to neutralize the nitric acid and form the highlyalkaline waste). In such an embodiment, the addition of CBPC precursorother than aluminum oxide may help bind both the sodium and nitratecomponents of the waste, as explained in more detail below. In suchapplications, it may be advantageous to mix the CBPC precursor, e.g.,MgO and at least a portion of the acidic phosphate with the waste ortime prior to the addition of the aluminum oxide. As in the proceedingembodiment, the mixer 30 may mix the resultant. For a period of time,e.g., 10-15 minutes, to allow the CBPC precursor reaction to proceed,after which the aluminum oxide and any remaining amount of the acidicphosphate may be added.

The mixing system 30 may continue to mix the slurry as water evaporatesfrom the reactants in the vessel 20. In addition to keeping thecomponents well-mixed, the mixing will help release water vapor from theslurry. This, in turn, will reduce voids in the solid waste form,increasing its strength and reducing its volume. In one embodiment ofthe invention, the pore volume of the final solid waste form, i.e., thetotal volume of the internal voids, is no greater than about 5% of thevolume of the solid waste form. In one particular embodiment, the porevolume is no greater than about 3 volume percent, with pore volumes ofno greater than about 1 volume percent being particularly advantageousfor many applications.

As the reaction proceeds and water is driven off, it will becomeincreasingly difficult to drive the mixer 35. In select embodiments ofthe invention, the mixing system 30 stops mixing the slurry when theslurry reaches a terminal consistency. This terminal consistency may bedetermined in a number of ways. In one embodiment, it may be determinedby monitoring a force required to drive the mixer 35 with the motor 32;once the requisite driving force reaches a predetermined limit, thecontroller 80 may terminate operation of the motor 32, allowing themixer 35 to stop. If so desired, the mixer 35 may then be lifted out ofthe reaction vessel 20 and reused for another reaction vessel. In oneparticular embodiment of the invention, though, the mixer 35 may be leftin the slurry as it hardens into the final solid waste form (discussedbelow in connection with FIG. 3). The releasable coupling 34 between themixer 35 and the motor 32 will facilitate separation of the solid wasteform, including the mixer 35, from the motor 32. A new mixer 35 may thenbe coupled to the motor 32 for processing the next batch of waste.

After mixing is terminated, the reactants in the slurry may be allowedto cure into a solid waste form. To enhance uniformity of the solidwaste form, the slurry at the terminal consistency should besufficiently stiff to avoid undue settling of the components of theslurry.

As explained above in connection with FIG. 2, some embodiments of theinvention may employ an aluminum hydrophosphate composition as theacidic phosphate in the acidic phosphate supply 40 in the wasteprocessing system 10 (FIG. 1). In accordance with one such embodiment,at least a portion of the aluminum oxide requirements of the slurry inthe waste processing vessel 20 may be combined with the acidic phosphatecomponent in a phosphate precursor slurry. For example, an aluminumoxide from an aluminum oxide supply 136 and an acidic phosphate from theacidic phosphate supply 130 may be added to the phosphate productionvessel 110 of the phosphate production system 100 (FIG. 2). This slurrymay be mixed with the mixer 120 to promote uniformity.

If so desired, the resultant slurry, which will comprise aluminumhydrophosphate, may be used in the acidic phosphate supply 40 of thewaste processing system 10 of FIG. 1. In other embodiments, the slurryin the phosphate production vessel 110 (FIG. 2) is at least partiallydried to form an acidic phosphate precursor that may be moreconcentrated and/or easier to handle. In one particular embodiment, thephosphate precursor slurry is dried sufficiently to form a paste or cakethat includes the aluminum hydrophosphate. In another particularembodiment, the phosphate precursor slurry is substantially completelydried, yielding a powdered phosphate precursor. Such pastes and powdersmay prove easier to store and use later in processing waste.

As noted above, some embodiments react an acidic phosphate and analuminum oxide at an elevated temperature, e.g., 130-200° C., to yieldanhydrous aluminum phosphates. To reduce the percentage of anhydrousaluminum phosphates in the phosphate precursor, the phosphate precursorslurry may be dried at a temperature of no greater than about 130° C.,e.g., at or below 100° C. In one particular embodiment, the aluminumoxide and the acidic phosphate are added to the phosphate productionvessel 110 at about room temperature. The reaction to form the aluminumhydrophosphate is an exothermic reaction and can increase thetemperature of the slurry. If necessary, the thermal control 150 may beused to maintain the slurry at a temperature of no greater than about130° C. over most or all of the reaction time.

As noted above, a molar ratio of aluminum to phosphorus in the wasteslurry is desirably greater than one, e.g., about 2-5. If so desired,the ratio of aluminum to phosphorus in the aluminum hydrophosphatecomposition may have the same Al:P ratio desired for the wasteprocessing step. In such an embodiment, the aluminum hydrophosphatecomposition would include both aluminum hydrophosphate and an excess ofaluminum oxide. It is believed that an aluminum hydrophosphatecomposition that includes a significant excess of aluminum oxide, e.g.,an Al:P ratio of two or greater, may be advantageously formed in atwo-step process. In one exemplary embodiment, a first-stage aluminumhydrophosphate composition having an Al:P ratio of about 0.95-1.1 isformed in accordance with the process outlined above. Thereafter, thefirst-stage aluminum hydrophosphate composition may be mixed with asufficient quantity of an aluminum oxide powder to increase the Al:Pratio to the desired level. In one particular implementation, thefirst-stage aluminum hydrophosphate composition is sufficiently dried toform a paste or a powder before mixing with the aluminum oxide powder.

Hence, an aluminum hydroxide composition in one embodiment may provideboth the acidic phosphate and the aluminum oxide employed in the wasteslurry. In such an embodiment, it is anticipated that the waste slurrywill have more water than the aluminum hydrophosphate composition. Ifthe waste is a liquid waste including water, this water may come fromthe waste itself. Otherwise, additional water may be added from thewater supply 56 to yield a suitable slurry and promote conversion of thealuminum hydrophosphate to an anhydrous aluminum phosphate at elevatedtemperatures.

In other embodiments of the invention, the Al:P ratio in the aluminumhydrophosphate composition is less than the Al:P ratio desired in thewaste slurry. If so desired, the Al:P ratio may be less than one,leaving an excess of the acidic phosphate in the aluminum hydrophosphatecomposition. In other embodiments, the Al:P ratio may be about one,yielding a substantially stoichiometric balance that may yield analuminum hydrophosphate composition that consists essentially ofaluminum hydrophosphate. In other embodiments, the Al:P ratio may begreater than one, but still less than the Al:P ratio desired in thewaste slurry. For example, the Al:P ratio in the aluminum hydrophosphatecomposition may be between about one and about two, e.g., about 1-1.1,yielding an aluminum hydrophosphate composition with an excess of thealuminum oxide.

D. Adaptations for Specific Waste Streams

As noted previously, some embodiments of the invention are particularlywell-suited for the long-term storage of radioactive wastes, includinghigh-level radioactive wastes. Even though the waste form may be stableand exhibit minimal radiolysis, the resultant solid waste form may stillgive off substantial radiation. In accordance with one particularembodiment, radiation-shielding components may be added to the wasteslurry. For example, boron may be added to the waste slurry (e.g., inthe form of ¹⁰B₄C) to help absorb neutrons and block gamma radiation.Hematite and/or magnetite may be added to the waste slurry to provide ameans to attenuate photons. Similarly, bismuth (III) oxide may be addedto the waste slurry to enhance the gamma-ray shielding properties of thesolid waste form. The addition of such components to other CBPCs (e.g.,magnesium potassium phosphates) for use as external radiation shields isdiscussed in PCT International Publication No. WO 02/069348, theentirety of which is incorporated herein by reference.

Wastes in certain embodiments of the invention may contain mercuryand/or chromium. For such wastes, it may be advantageous to add aquantity of a sulfiding agent, e.g., less than about 1 weight percent,preferably no greater than about 0.5 weight percent, Na₂S, to convertthe metals into their sulfides. Such sulfides tend to be more stable andless likely to leach from the final waste form. Similarly, a reductant,e.g., less than 1 weight percent, preferably no greater than about 0.5weight percent, SnCl₂, may be added to wastes containing technetium. Asdiscussed in U.S. Pat. No. 6,133,498 (Singh et al., the entirety ofwhich is incorporated herein by reference), the SnCl₂ or the like canlimit the leaching of technetium from the final waste form. It is alsoanticipated that 0.5 weight percent or less of the tin chloride canreact with any mercury and/or chromium in the waste to form a stablechloride. Hence, it may be possible to omit the use of Na₂S even inwastes that contain mercury and/or chromium. In one embodiment, theheavy metals are given a period of time to react with the sulfidingagent and/or reductant before completing the conversion of the aluminumoxide to aluminum phosphate. Hence, in one embodiment, the slurry ismixed at a temperature of no greater than about 130° C. for a period oftime, e.g., 10-15 minutes. Thereafter, the slurry may be heated to ahigher temperature, e.g., about 140-200° C., to promote formation ofAlPO₄.

One advantage of select embodiments of the invention is the ability toreadily handle salt-bearing wastes, alkaline wastes, and acidic wastes.Although salt-bearing wastes can be particularly problematic when usingportland cements or the like, most salts should have little effect onthe formation of the AlPO₄ matrix discussed above. Alkaline wastes canalso be handled fairly readily simply by increasing the quantity ofacidic phosphate added to the waste slurry. For example, a small amountof phosphoric acid may be added to the slurry to bring the slurry to anacceptable pH level. In an analogous fashion, acidic wastes can beeffectively neutralized to acceptable pH levels by adding additionaloxides to the waste slurry. In one embodiment, this additional oxide maycomprise an additional quantity of aluminum oxide, e.g., Al₂O₃ and/orAl(OH)₃, or magnesium oxide, which is explained above as facilitatingtreatment of nitrate-containing wastes. As noted previously, other wastestreams may be highly alkaline. As one example, some acidic wastesincluding high concentrations of nitric acid have been neutralized andrendered alkaline by the addition of NaOH, leaving both sodium andnitrates in the waste.

Some waste streams are highly acidic. For example, waste streams fromplutonium extraction or other nuclear material processing approaches mayinclude high concentrations of nitric acid. In many conventionalprocesses, including cementation and pozzolonic processes, sodium andnitrates are both highly leachable. In thermal processes, sodium andnitrates are both highly corrosive and may volatilize. It has been foundthat the use of at least some CBPCs can substantially reduce theleaching of sodium and nitrates from a waste form. In one embodiment,therefore, a CBPC precursor other than an aluminum oxide is mixed with awaste, either prior to or concurrently with the addition of the aluminumoxide and/or to the acidic phosphate to the waste slurry. In oneparticular example, the CBPC percursor comprises calcined MgO and theacidic phosphate comprises monopotassium phosphate (KH₂PO₄), which canyield a CBPC that comprises magnesium potassium phosphate hexahydrate(MgKPO₄.6H₂O). As discussed in U.S. Provisional Application 60/450,563(the entirety of which is incorporated herein by reference) the MgO isbelieved to form a CBPC that can help effectively bind or incorporateboth sodium and nitrates, including both MgNaPO₄OnH₂O and KNO₃.

In another embodiment noted above, the CBPC precursor comprises calcinedMgO and is added prior to the addition of the acidic phosphate, formingMgNO₃ ₂, which will tend to form small particles. These small,relatively insoluble particles may be bound within the AlPO₄ matrix. Ifan excess of MgO is employed, it may react with the acidic phosphate toform a magnesium phosphate.

Safely forming solid waste forms from oily wastes has been particularlyproblematic in some applications. In accordance with embodiments of thepresent invention, the oily wastes may be effectively cleaned withphosphoric acid, which may act as a detergent and break down the oilywastes. Premixing the oily waste with phosphoric acid will help breakdown the waste, and this premix may be added to the waste slurry.Alternatively, an additional quantity of acidic phosphate,advantageously phosphoric acid, may be added to the waste slurry tobreak down the oily waste in the waste processing vessel 20 (FIG. 1). Ifso desired, the waste slurry in such an embodiment may be mixed for atime below 130° C., e.g., below about 100° C., for a time before heatingit to a higher second temperature, e.g., 140-175° C.

Embodiments of the invention also effectively handle carbonate-bearingwastes. In some known processes, the generation of carbon dioxide fromcarbonates may form undesirable voids in the solid waste form. As notedabove, mixing the waste slurry in accordance with embodiments of theinvention allows water vapors to escape the slurry. This same mixing mayalso allow any generated CO₂ to be released prior to curing of the solidwaste form.

E. Solid Waste Forms

The waste slurry may be allowed to cure in any suitable shape. Forexample, the waste slurry may be removed from the waste processingvessel 20 via the outlet 72 and cast into suitable sizes and shapesusing known casting techniques.

FIG. 3 schematically illustrates a solid waste form 200 in accordancewith one particular embodiment of the invention. The solid waste form200 is indicative of a solid waste form that may be produced using thewaste processing system 10 shown in FIG. 1. In this embodiment, thewaste processing vessel 20 and the mixer 35 may be incorporated in thesolid waste form 200. A majority of the mixer 35 may be embedded in thesolid ceramic 210 resulting from the reactions outlined above. Thevolume of the solidified ceramic may be less than the total volume ofthe waste slurry due to driving off the water in the waste slurry. Thismay leave a head space 215 between the solid ceramic 210 and the top ofthe waste processing vessel 20.

If so desired, the head space 215 may be partially or fully filled witha “clean” material such as a waste-free CBPC, an organic resin, or acastable cement to limit exposure of the ceramic 210 to the elements. Inan alternative approach, some or all of the head space 215 may be filledwith an additional quantity of a waste-bearing anhydrous aluminumphosphate composition. In one particular embodiment, the additionalquantity of the waste-bearing aluminum phosphate composition may beprepared generally as outlined above in a second waste processing vessel20 (FIG. 1). When the slurry in the second waste processing vessel 20 isdried to a desired level, e.g., when it reaches a putty-likeconsistency, it may be added to the head space 215 in the first wasteprocessing vessel 20 (FIG. 3). In one particular embodiment, thematerial from the second vessel 20 may be added to the head space 215before the material in the first vessel 20 is allowed to completelycure. This may promote bonding of the added material to the materialalready present in the vessel, forming a solid ceramic 210 thatsubstantially fills the volume of the waste processing vessel 20.

The ceramic 210 will generally include a matrix with particles embeddedtherein. The matrix will comprise an anhydrous aluminum phosphate, e.g.,aluminum orthophosphate (AlPO₄) with minor amounts of aluminummetaphosphate (Al(PO₃)₃). Although the matrix may also include aluminumhydrophosphates, the proportion of the hydrophosphate in the matrix isdesirably kept relatively low or substantially eliminated. The anhydrousaluminum phosphate matrix may also bind components of the waste in theceramic 210. For example, if the waste stream includes heavy metals, thematrix may bind phosphates of the heavy metals. If the waste includesparticulate matter, these particles may be distributed as discreteparticles within the matrix and may be substantially encapsulated in thematrix. If the waste comprises a radioactive waste, the radioactivewaste will typically be distributed in the matrix. In one embodiment,the components of the waste are substantially uniformly distributed inthe matrix.

As noted above, the molar ratio of aluminum to phosphorus in the wasteslurry is desirably greater than one. This will leave an excess of thealuminum oxide in the solid waste form. Typically, the aluminum oxidewill start as a particulate component, e.g., particles of alumina. Thesealuminum oxides may be distributed in the matrix and may beadvantageously distributed substantially uniformly throughout thematrix. It is believed that these aluminum oxide particles within thephosphate matrix will enhance the mechanical properties of the solidceramic 210 and, hence, the waste form 200.

In one embodiment noted above, a CBPC precursor other than an aluminumoxide, e.g., an oxide of magnesium or another metal, may be added to theslurry. Particularly if this CBPC precursor is allowed an opportunity toreact with a nitric acid-laden waste prior to addition of the aluminumoxide and the acidic phosphate, it is anticipated that the CBPCprecursor will form particles of a metal nitrate, e.g., Mg(NO₃)₂ if theCBPC comprises MgO. The particles are expected to remain in the slurryand, ultimately, in the final waste form. If an alkaline waste includingNa and NO₃ ⁻ is treated with a magnesium oxide and an acidic phosphate,the resultant magnesium phosphate may define particles that are embeddedin the anhydrous aluminum phosphate matrix in the waste form.Investigation and characterization of such a magnesium oxide-based CBPCis still being characterized, but it is currently surmised that at leasta portion of this specific CBPC takes a pseudo-hydroxyapatite form,e.g., MgNa(PO₄).nH₂O. If nitrates are present in the slurry, this CBPCmay also or instead form a nitrated apatite-type mineral not previouslyreported in the literature. Hence, the waste form in this particularexample may comprise one or both of a) a pseudo-hydroxyapatite includingmagnesium and sodium and b) a nitrated apatite including sodium andnitrate in a matrix that includes an anhydrous aluminum phosphate.

In one particular embodiment, the amount of magnesium oxide addedexceeds the stoichiometric amount needed to react with the nitridesand/or other compounds in the waste. If a superstoichiometric amount ofaluminum oxide is also added to the slurry, the resultant waste form mayinclude particulate aluminum oxide and magnesium oxide. It is believedthat the magnesium oxide will react with hydrogen in the waste form.Hence, if radiolysis of water generates any hydrogen gas, the excessmagnesium oxide may serve as a getter, reducing the risks noted aboveassociated with radiolysis.

The above-detailed embodiments and examples are intended to beillustrative, not exhaustive, and those skilled in the art willrecognize that various equivalent modifications are possible within thescope of the invention. For example, whereas steps are presented in agiven order, alternative embodiments may perform steps in a differentorder. The various embodiments described herein can be combined toprovide further embodiments.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification unless the preceding description explicitly definessuch terms. The inventors reserve the right to add additional claimsafter filing the application to pursue additional claim forms for otheraspects of the invention.

1. A method of processing waste, comprising: combining a waste componentwith an aluminum oxide and an acidic phosphate component in a slurrycomprising water, wherein the waste component comprises hazardous wasteand a molar ratio of aluminum to phosphorous in the slurry is greaterthan one; evaporating water in the slurry while mixing the slurry at afunctional temperature of about 140-200° C.; and allowing the mixedslurry to cure into a solid waste form comprising an anhydrous aluminumphosphate with a residual portion of the waste component bound therein.2-5. (canceled)
 6. The method of claim 1 wherein the anhydrous aluminumphosphate comprises aluminum orthophosphate.
 7. The method of claim 1wherein the waste component comprises a heavy metal, further comprisingmixing the slurry at a temperature of no greater than about 130° C. fora first time before mixing the slurry at the functional temperature. 8.(canceled)
 9. The method of claim 1 wherein the acidic phosphatecomponent comprises phosphoric acid or aluminum hydrophosphate. 10-11.(canceled)
 12. The method of claim 1 wherein the aluminum oxidecomprises aluminum hydroxide or anhydrous Al₂O₃. 13-17. (canceled) 18.The method of claim 1 wherein the aluminum oxide and the acidicphosphate component are combined prior to combining with the wastecomponent. 19-20. (canceled)
 21. The method of claim 1 wherein theslurry comprises a waste slurry and wherein combining the wastecomponent, the aluminum oxide, and the acidic phosphate component in thewaste slurry comprises: reacting at least a portion of the aluminumoxide with the acidic phosphate component in a phosphate precursorslurry; at least partially drying the phosphate precursor slurry to forma phosphate precursor comprising a paste or a powder; and after at leastpartially drying the phosphate precursor slurry, mixing the phosphateprecursor with the waste component in the waste slurry, the waste slurryhaving more water than the phosphate precursor prior to the evaporationof the water in the waste slurry.
 22. (canceled)
 23. The method of claim1 further comprising terminating the mixing upon reaching a terminalconsistency. 24-27. (canceled)
 28. The method of claim 1 whereincombining in the slurry further comprises combining a CBPC precursorother than an aluminum oxide with the waste component and the acidicphosphate in the slurry and, thereafter, adding the aluminum oxide tothe slurry.
 29. The method of claim 1 wherein the waste component isstored in a waste storage container and wherein the waste component,aluminum oxide, and acidic phosphate component are combined in the wastestorage container.
 30. The method of claim 1 wherein the slurry furthercomprises at least one of SnCl₂ and Na₂S.
 31. (canceled)
 32. A method ofproducing a stable waste form, comprising: reacting an aluminum oxidewith an acidic phosphate component in a first slurry; at least partiallydrying the first slurry at a first temperature to form a phosphateprecursor; mixing the phosphate precursor and a waste in a second slurryat a second temperature of about 106-175° C. while allowing water in thesecond slurry to evaporate; after at least a majority of the water inthe second slurry is evaporated, allowing the mixed second slurry tocure into a solid waste form including a remaining portion of thealuminum oxide distributed in a matrix comprising an anhydrous aluminumphosphate and at least a portion of the waste. 33-40. (canceled)
 41. Themethod of claim 32 wherein a molar ratio of aluminum to phosphorous inthe waste form is greater than one and no greater than about
 5. 42-43.(canceled)
 44. The method of claim 32 wherein mixing the second slurrycomprises mixing the second slurry in a container with a mixer andallowing the mixed second slurry to cure in the container. 45-46.(canceled)
 47. The method of claim 32 wherein mixing the second slurryfurther comprises mixing a CBPC precursor other than an aluminum oxidein the second slurry.
 48. The method of claim 32 wherein mixing thesecond slurry further comprises mixing a magnesium oxide in the secondslurry. 49-50. (canceled)
 51. The method of claim 32 further comprisingmixing the second slurry at a third temperature for a first time beforemixing the second slurry at the second temperature, wherein the secondtemperature is higher than the third temperature.
 52. A method ofproducing a stable, low-volume waste form from a radioactive material,comprising: mixing the radioactive material with an aluminum oxide andan acidic phosphate to form a slurry, a molar ratio of aluminum tophosphorous in the slurry being between about 2 and about 5, and thealuminum oxide comprising hydrous alumina, anhydrous alumina, oraluminum hydroxide; heating the slurry to a first temperature that is nogreater than about 200° C., but is at least as great as a dissolutiontemperature of the aluminum oxide with the acidic phosphate; whilemixing the slurry, evaporating water from the slurry at a secondtemperature of about 140-175° C. until a substantial majority of thewater is evaporated; after the water evaporation, allowing the resultantevaporated product to cure as a solid waste form comprising aluminumoxide particles and at least a portion of the radioactive waste in amatrix comprising substantially anhydrous AlPO₄. 53-62. (canceled) 63.The method of claim 52 further comprising adding a CBPC precursor otherthan an aluminum oxide to the slurry. 64-65. (canceled)
 66. The methodof claim 52 wherein the radioactive material is stored in a wastestorage container and wherein the slurry is mixed in the waste storagecontainer. 67-68. (canceled)
 69. A solid waste form comprising: a matrixcomprising a substantially anhydrous aluminum phosphate and a phosphateof a heavy metal; a radioactive material distributed in the matrix; andaluminum oxide particles distributed in the matrix.
 70. The solid wasteform of claim 69 further comprising a mixer imbedded in the matrix. 71.The solid waste form of claim 69 wherein at least a portion of theradioactive material comprises particles of radioactive materialencapsulated in the matrix.
 72. The solid waste form of claim 69 furthercomprising magnesium oxide distributed in the matrix.
 73. The method ofclaim 1 wherein the waste has a first pH level, and further comprisingadding a neutralizing material to the waste before allowing the mixedslurry to cure to at least partially neutralize the waste so the wastehas a second pH level different from the first pH level.
 74. The methodof claim 73 wherein the neutralizing material is added to the wastebefore the waste is combined with the aluminum oxide and the acidicphosphate.
 75. The method of claim 1, further comprising adding at leastone of a beta-absorptive, gamma-absorptive, alpha-absorptive, orneutron-absorptive material directly to the waste before allowing themixed slurry to cure.
 76. The method of claim 75 wherein the at leastone of a beta-absorptive, gamma-absorptive, alpha-absorptive, orneutron-absorptive material is added to the waste before the waste iscombined with the aluminum oxide and the acidic phosphate.
 77. Themethod of claim 1, further comprising dewatering the waste during orbefore the waste is combined with the aluminum oxide and the acidicphosphate.
 78. The method of claim 1, further comprising adding aneutralizing material to the waste to at least partially neutralize thewaste before the waste is combined with the aluminum oxide and theacidic phosphate.
 79. The method of claim 78 wherein the neutralizingmaterial is added before the evaporating the water.
 80. The method ofclaim 78 wherein the neutralizing material is added after evaporatingthe water, and mixing occurs after adding the neutralizing material. 81.The method of claim 1, further comprising adding an H2 getter agent tothe waste or the slurry to reduce H2 gas generation.
 82. The method ofclaim 1 wherein the H2 getter agent include MgO.
 83. The method of claim1 wherein the waste is an acidic waste, further comprising neutralizingthe waste with at least one metal oxide.
 84. The method of claim 1,further comprising adding a salt to the slurry to control reaction ratesduring mixing of the slurry.
 85. The method of claim 1, furthercomprising adding at least one of a stabilizing agent and a reactantagent to the waste or the slurry.
 86. The method of claim 1, furthercomprising adding an exothermic agent to at least one of the waste andthe slurry that reacts to create heat that heats the at least one of thewaste and the slurry.
 87. The method of claim 1, further comprisingadding to least one of the waste and the slurry a shielding agent forneutrons, alpha particles, beta particles, or gama particles in thewaste to provide an at least partially self-shielding waste.